Head drum device and magnetic recorder/reproducer

ABSTRACT

A head drum device of the present invention prevents a magnetic tape ( 2 ) from clinging to the head drum device ( 3 ) due to electrostatic charge by using a carbon-containing synthetic resin as the material of an upper drum ( 33 ) in order to reduce the manufacturing cost for the upper drum. Also, setting the outside diameter of the upper drum ( 33 ) smaller than that of an intermediate drum ( 32 ) eliminates the need for a high-level of manufacturing precision in the manufacture of the upper drum ( 33 ). Thus, it is possible to reduce the manufacturing cost for the upper drum ( 33 ).

TECHNICAL FIELD

[0001] The present invention relates to a head drum device forperforming either or both of writing and reading of a signal to and froma magnetic tape and to a magnetic recording/playback apparatus includingthis head drum device. More particularly, the present invention isdirected to a head drum device having a three-layered structure in whichan intermediate drum is rotatable and also to a magneticrecording/playback apparatus including this head drum device.

BACKGROUND ART

[0002] In recent years, video tape recorders have come into widespreaduse as magnetic recording/playback apparatuses using magnetic tape as arecording medium. In video tape recorders, a helical scan method, inwhich recording or playback of a signal is performed by helicallywinding a magnetic tape around a head drum device which is provided witha rotatable magnetic head on its circumference, is commonly used. Thehead drum device used in such video tape recorders is generally of twotypes: one having a two-layered structure including a fixed lower drumand a rotatable upper drum having a magnetic head; the other having athree-layered structure including a fixed lower drum, a rotatableintermediate drum having a magnetic head, and a fixed upper drum.

[0003]FIG. 1 illustrates an example of the configuration of aconventional three-layered head drum device.

[0004]FIG. 1 is a side view of a conventional head drum device 40 havinga three-layered structure. The head drum device 40 includes a fixedlower drum 31, an intermediate drum 32 rotatable coaxially with thelower drum 31, and an upper drum 43 fixed coaxially with theintermediate drum 32. The lower drum 31 is provided with a lead 31 aaround its circumference for assisting the helically wound magnetic tape2 to travel. A motor mechanism and associated parts for rotating anddriving the intermediate drum 32 are contained within the lower drum 31.On the other hand, on the circumference of the intermediate drum 32,magnetic heads 32 a for writing or reading a signal to and from themagnetic tape 2 are mounted. In practice, a plurality of (two or four)magnetic heads 32 a is usually mounted. A rotary transformer or the likeserving as a signal transmission path between the magnetic head 32 a andan external device is accommodated within the upper drum 43.

[0005] While a recording or playback operation is performed on themagnetic tape 2 in such a head drum device 40, as shown in FIG. 1, themagnetic tape 2 is guided by the lead 31 a and travels while being woundaround the circumference of the head drum device 40 at a predeterminedangle. At this time, the intermediate drum 32 is rotated and themagnetic head 32 a scans the magnetic tape 2 at an angle, thusperforming writing and reading of signals. The upper drum 43 also servesto prevent the traveling magnetic tape 2 from being displaced upwardlyto cover the head drum device 40.

[0006] In the three-layered head drum device 40, as shown in FIG. 1, theaxial length of the rotatable intermediate drum 32 is smaller than thewidth of the magnetic tape 2, thereby the magnetic tape 2 is woundaround three layers, that is, the lower drum 31, the intermediate drum32, and the upper drum 43. In contrast, in a head drum device having atwo-layered structure including a fixed lower drum and a rotatable upperdrum, the axial length of the upper drum is substantially equal to thewidth of the magnetic tape 2. Such a two-layered head drum device may beprovided with a tape guide above the upper drum to prevent the magnetictape 2 from covering the upper drum, thus often having an apparentthree-layered structure. However, the structure of this type is alsocalled a two-layered structure here. On the other hand, the structure inwhich the axial length of the intermediate drum 32 is smaller than thewidth of the magnetic tape 2 is called a three-layered structure.

[0007] A specific example of the head drum device 40 having athree-layered structure is shown in Japanese Unexamined PatentApplication Publication No. 10-340504 which discloses a head drum devicewith good contact characteristics between the magnetic tape 2 and themagnetic head 32 a. In the head drum device 40, rotating theintermediate drum 32 at high speed while a recording or playbackoperation is performed causes air to be sucked in by the force ofrotation to form an air film between the outer peripheral surface andthe magnetic tape 2. This air film allows the magnetic tape 2 to travelsmoothly. However, this air film tends to have a thickness distributionsuch that it is thicker at an entry side of the magnetic tape 2 andthinner at an exit side thereof. In such a case, the contact pressurebetween the magnetic tape 2 and the magnetic head 3 is not uniform, sothat accurate writing and reading of a signal to and from the magnetictape are prevented. On the other hand, in the above-mentionedpublication, such a problem is solved by bonding a belt-like metallicthin film on the lower drum 31 on the side where the magnetic tape 2exits to form a projection.

[0008] In the head drum device 40 having a three-layered structure, inthe course of using a tape cassette that feeds the magnetic tape 2, forexample, the magnetic tape 2 may be charged with static electricity sothat the magnetic tape 2 is attracted to the head drum device 40 andclings to it when this tape cassette is loaded. If the magnetic tape 2travels in such a condition, a sufficient air film cannot be generatedbetween the outer peripheral surface of the head drum device 40 and themagnetic tape 2, which may cause the magnetic tape 2 to be damaged.Particularly, in the head drum device 40 having a three-layeredstructure, as described above, since the axial length of thecircumference of the rotatable intermediate drum 32 is small, asufficient air film fails to be generated when the magnetic tape 2travels. Accordingly, the magnetic tape 2 is prone to cling to the headdrum device 40.

[0009] Therefore, the conventional head drum device 40 having athree-layered structure has prevented electrostatic charge by using anon-magnetic metal, such as an aluminum alloy or a copper alloy, as thematerial of the upper drum 43. Further, in the conventional head drumdevice 40 with a three-layered structure, the intermediate drum 32 hasbeen formed in such a manner that its outside diameter is equal to thatof the upper drum 43, and the friction resistance has been restricted bymaking the surface on which the magnetic tape 2 travels smooth. Also, inorder to prevent the magnetic tape 2 from being damaged when it is incontact with the outer peripheral surface of the upper drum 43, thesurface of the upper drum 43 has been manufactured using the metallicmaterial mentioned-above formed with a precision of ±2 μm. However,since manufacture of the upper drum 43 described above requiresexpensive materials, processing, equipment, and so on, use of asynthetic resin material whose cost is relatively low has beendiscussed.

[0010] However, the upper drum 43 made of a synthetic resin has highresistance so that static electricity is likely to be charged, andtherefore the magnetic tape 2 is prone to cling to the upper drum.Further, the manufacturing precision of the surface dimensions islargely reduced in injection molding of synthetic resin material,comparing with that of metallic material. Accordingly, since furtherreduction of the outside diameter by machining is necessary in order toobtain a manufacturing precision falling within the range of ±2 μm thatis required when manufacturing the upper drum 43, it is impossible toreduce the manufacturing costs.

[0011] Furthermore, in a magnetic recording/playback apparatus includingthe head drum device 40, when any stains or dust is attached on theouter peripheral surface of the upper drum 43, the surface of themagnetic tape 2 may be damaged. Thus, actions such as mounting parts forremoving such stains or dust, managing the manufacturing process so asto prevent such stains or dust from being attached, cleaning, and so onhave been required during the manufacturing process. As a result, themanufacturing costs have increased due to the increased number ofmanufacturing processes, additional equipment, and material costs forchemical agents such as alcohol used for cleaning, which are necessaryfor such actions.

[0012] The present invention is provided in order to solve such problemsand an object of the present invention is to provide a head drum devicehaving reduced manufacturing cost for the upper drum.

[0013] Another object of the present invention is to provide a magneticrecording/playback apparatus provided with a head drum device havingreduced manufacturing cost for the upper drum.

DISCLOSURE OF INVENTION

[0014] In order to solve the problems described above, the presentinvention provides, in a head drum device for performing either or bothof writing and reading of a signal to and from a magnetic tape, the headdrum device is characterized by comprising: a fixed lower drum having alead for helically guiding the magnetic tape; an intermediate drumhaving a magnetic head on its outer peripheral surface, which is rotatedand supported coaxially with the lower drum and is formed in such amanner that the axial length of the outer peripheral surface is smallerthan the width of the magnetic tape; and an upper drum made of asynthetic resin containing carbon, which is fixed and supportedcoaxially with the intermediate drum.

[0015] In such a head drum device, use of carbon-containing syntheticresin as the material of the upper drum can prevent the magnetic tapefrom clinging to the head drum device due to electrostatic charge. Also,setting the outside diameter of the upper drum smaller than that of theintermediate drum can eliminate the need for a high-level ofmanufacturing precision in the manufacture of the upper drum. Thus, itis possible to reduce the manufacturing cost for the upper drum.

[0016] Also, the present invention provides, in a magneticrecording/playback apparatus for performing either or both recording andplayback of a signal on a magnetic tape, the magnetic recording/playbackapparatus is characterized by having a head drum device comprising: afixed lower drum having a lead for helically guiding the magnetic tape;an intermediate drum having a magnetic head on its outer peripheralsurface, which is rotated and supported coaxially with the lower drumand is formed in such a manner that the axial length of the outerperipheral surface is smaller than the width of the magnetic tape; andan upper drum made of a synthetic resin containing carbon, which isfixed and supported coaxially with the intermediate drum.

[0017] In such a magnetic recording/playback apparatus, use ofcarbon-containing synthetic resin as the material of the upper drum ofthe head drum device can prevent the magnetic tape from clinging to thehead drum device due to electrostatic charge. Also, setting the outsidediameter of the upper drum smaller than that of the intermediate drumcan eliminate the need for a high-level of manufacturing precision inthe manufacture of the upper drum. Thus, it is possible to reduce themanufacturing cost for the upper drum.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG 1. illustrates an example of the configuration of aconventional three-layered head drum device.

[0019]FIG. 2 is a schematic diagram showing the configuration of a headdrum device according to the present invention.

[0020]FIG. 3 is a schematic diagram showing the configuration of amagnetic recording/playback apparatus including a head drum deviceaccording to the present invention.

[0021]FIG. 4 is an enlarged view of the portion encircled by A in FIG.2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] An embodiment of the present invention will be described belowwith reference to the accompanying drawings. FIG. 3 schematicallyillustrates the configuration of a magnetic recording/playback apparatusincluding a head drum device according to the present invention.

[0023]FIG. 3 illustrates a schematic diagram of a traveling system for amagnetic tape 2 in the magnetic recording/playback apparatus 1 in arecording or playback mode. The traveling system for the magneticrecording/playback apparatus 1 includes a head drum device 3 forperforming either or both of writing and reading of a signal to and fromthe magnetic tape 2, a capstan 4 and a pinch roller 5 for making themagnetic tape 2 travel at a predetermined speed, and a plurality of tapeguides (shown as TG in FIG. 3) 6 to 11 for assisting the magnetic tape 2to travel. One example of this magnetic recording/playback apparatus 1is a video tape recorder that records or plays back images and voicesignals in digital form. A tape cassette 12 that is received in themagnetic recording/playback apparatus 1 includes a feed reel 12 a and atake-up reel 12 b for the magnetic tape 2.

[0024] While a recording or playback operation is performed, themagnetic tape 2 is led out from the feed reel 12 a by the force of thecapstan 4, the pinch roller 5, and the take-up reel 12 b, and is woundaround the head drum device 3 via the tape guides 6, 7, and 8. Themagnetic tape 2 can be wound around the head drum device 3 at apredetermined angle to perform writing and reading of signals with therotatable magnetic head by mounting the tape guides 8 and 9 at a tiltand by providing a lead for guiding the magnetic tape 2 on the outerperipheral surface of the head drum device 3. The magnetic tape 2 isthen wound around the take-up reel 12 b via the tape guides 9 and 10,the capstan 4 and pinch roller 5, and the tape guide 11.

[0025] Next, the head drum device 3 will be described in detail. FIG. 2schematically illustrates the configuration of the head drum device 3according to the present invention.

[0026]FIG. 2 is a side view of the head drum device 3 included in themagnetic recording/playback apparatus 1. The head drum device 3 hasthree layers, that is, a fixed lower drum 31, an intermediate drum 32rotatable coaxially with the lower drum 31, and an upper drum 33 fixedcoaxially with the intermediate drum 32. The lower drum 31 has acylindrical circumference and is provided with a lead 31 a for assistingthe magnetic tape 2 to travel, which is helically wound around thiscircumference. A motor mechanism and associated parts (not shown) forrotating and driving the intermediate drum 32 are contained within thelower drum 31. On the other hand, the intermediate drum 32 has acylindrical circumference with the same outside diameter as that of thecircumference of the lower drum 31, on which magnetic heads 32 a forperforming writing and reading of a signal to and from the magnetic tape2 are mounted. In practice, a plurality of (two or four) magnetic heads32 a is mounted on the circumference of the intermediate drum 32, and isrotated together with the intermediate drum 32. Further, the axiallength of the intermediate drum 32 is smaller than the width of themagnetic tape 2. The upper drum 33 has a circumference that is a part ofthe cylindrical shape and is formed in such a manner that the radius ofthis circumference is smaller than that of the circumference of theintermediate drum 32. Also, a rotary transformer or the like (not shown)serving as a signal transmission path between the magnetic head 32 a andan external device is accommodated within the upper drum 33.

[0027] While a recording or playback operation is performed on themagnetic tape 2 in such a head drum device 3, as shown in FIG. 2, themagnetic tape 2 is guided by the lead 31 a and travels while being woundaround the circumference of the head drum device 3 at a predeterminedangle. At this time, the intermediate drum is rotated and the magnetichead 32 a scans the magnetic tape 2 at an angle, thus performing writingand reading of signals. Further, as described above, because the axiallength of the intermediate drum 32 is smaller than the width of themagnetic tape 2, the magnetic tape 2 travels while being wound aroundthree layers, that is, the lower drum 31, the intermediate drum 32, andthe upper drum 33.

[0028] In this head drum device 3, the upper drum 33 is made of asynthetic resin containing carbon. The fact that it contains carbongives the upper drum 33 conductivity, thus suppressing electrostaticcharge. In the magnetic recording/playback apparatus 1, the magnetictape 2, for example, is likely to be charged with static electricityduring use. If the upper drum 33 is charged with static electricity dueto such a reason, the upper drum 33 and the magnetic tape 2 may clingtogether, thus hampering smooth travel of the magnetic tape 2.Meanwhile, because synthetic resins do not normally have conductivity,the present invention can avoid electrostatic charge by including carbonin the resin. Therefore, the value of the surface resistance of theupper drum 33 formed is usually 1015 Ω or less and the carbon content is10 percent by weight or more. Examples of synthetic resins used includepolycarbonate, ABS (acrilonitrile-butadiene-styrene) resin, and POM(polyoxymethylene). A carbon content of 30 percent by weight may beoptimal from the viewpoint of conductive performance and cost incurrently distributed products.

[0029] In order to reduce manufacturing costs compared with conventionaldevices, the head drum device 3 using such materials is desirablymanufactured only by means of injection molding without subsequentprocessing. However, since the manufacturing precision achieved by meansof injection molding of the above-mentioned synthetic resin is around±10-20 μm, the required level of manufacturing precision is not providedwhen the upper drum 33 and the intermediate drum 32 are formed so as tohave the same diameter. Accordingly, in the head drum device 3 of thepresent invention, the upper drum 33 is formed in such a manner that itsoutside diameter is smaller than that of the intermediate drum 32. Thus,the present invention can realize reduced manufacturing cost byintentionally decreasing the outside diameter of the upper drum 33 so asto decrease the required manufacturing precision to the level availablein injection molding of synthetic resin.

[0030]FIG. 4 is an enlarged view of the portion encircled by A in FIG.2.

[0031] As shown in FIG. 4, while a recording or playback operation isperformed on the magnetic tape 2 in the head drum device 3, traveling ofthe magnetic tape 2 and rotation of the intermediate drum 32 cause airto be sucked in between both the intermediate drum 32 and upper drum 33and the magnetic tape 2 to form an air film 34. Further, the head drumdevice 3 is formed in such a manner that the outer peripheral surface ofthe upper drum 33 recedes inwardly from that of the intermediate drum 32by the amount of a step d, that is, the radius of the circumference ofthe upper drum 33 is smaller than that of the intermediate drum 32 bythe amount d.

[0032] On the other hand, any stains or dust attached on the surface ofthe upper drum 33 may attach onto the magnetic tape 2 during stopping oroperating, which results in the magnetic tape 2 clinging to the headdrum device 3, thereby causing obstructing the travel of the magnetictape 2. Such clinging of the magnetic tape 2 is likely to occur when thestep d between the upper drum 33 and the intermediate drum 32 is 10 μmor less. Moreover, formation of the air film 34 mentioned above allowsthe magnetic tape 2 to travel smoothly and to come into contact with themagnetic head 32 a at an appropriate pressure. However, it is moredesirable that the step d between the outer peripheral surface of theupper drum 33 and that of the intermediate drum 32 does not exceed 100μm in order to sufficiently form the air film 34.

[0033] Therefore, an appropriate value of the step d is not less than 10μm and preferably falls within the range from 10 to 100 μm. Consideringthe manufacturing precision of synthetic resin by injection molding,when the target value for the step d formed is set to around 50 to 60μm, it becomes possible to easily form the upper drum 33 using syntheticresin materials containing carbon, as described above.

[0034] As described above, in the head drum device 3 of the presentinvention, use of synthetic resin with a carbon content of 10 percent byweight or more as the material of the upper drum 33 can prevent the headdrum device 3 and the magnetic tape 2 from clinging together due toelectrostatic charge, thus considerably reducing the cost of thematerial. Also, setting the radius of the outer peripheral surface ofthe upper drum 33 smaller than that of the intermediate drum 32 by anamount of 10 to 100 μm eliminates the need for a high-level ofmanufacturing precision in the manufacture of the upper drum 33.Moreover, such setting also can reduce the possibility that any stainsor dust attached on the upper drum 33 may be transferred to the magnetictape 2, so that the need for a process or mechanism for removing suchstains or dust is eliminated. Thus, the upper drum 33 can bemanufactured using materials mentioned above by injection molding, sothat the need for high-precision processing machines can be eliminatedto reduce the cost of equipment and also to reduce the cost ofmanufacture.

[0035] Moreover, a device including the head drum device of the presentinvention is not limited to a video tape recorder. The present inventioncan be applied to all helical-scan-type magnetic recording apparatusesand magnetic playback apparatuses using a magnetic tape as a recordingmedium.

[0036] As described above, in the head drum device of the presentinvention, use of carbon-containing synthetic resin as the material ofthe upper drum can prevent the magnetic tape from clinging to the headdrum device due to electrostatic charge. Also, setting the outsidediameter of the upper drum smaller than that of the intermediate drumeliminates the need for a high-level of manufacturing precision in themanufacture of the upper drum. Thus, it is possible to reduce themanufacturing cost for the upper drum.

[0037] Also, in the magnetic recording/playback apparatus of the presentinvention, use of carbon-containing synthetic resin as the material ofthe upper drum of the head drum device can prevent the magnetic tapefrom clinging to the head drum device due to electrostatic charge. Also,setting the outside diameter of the upper drum smaller than that of theintermediate drum eliminates the need for a high-level of manufacturingprecision in the manufacture of the upper drum. Thus, it is possible toreduce the manufacturing cost for the upper drum.

1. In a head drum device for performing either or both writing andreading of a signal to and from a magnetic tape, said head drum deviceis characterized by comprising: a fixed lower drum including a lead forhelically guiding said magnetic tape; an intermediate drum including amagnetic head on the outer peripheral surface thereof, which is rotatedand supported coaxially with said lower drum and is formed in such amanner that the axial length of said outer peripheral surface is smallerthan the width of said magnetic tape; and an upper drum made of asynthetic resin containing carbon, which is fixed and supportedcoaxially with said intermediate drum.
 2. The head drum device accordingto claim 1, characterized in that the outside diameter of said upperdrum is smaller than that of said intermediate drum.
 3. The head drumdevice according to claim 2, characterized in that the circumference ofsaid upper drum differs in radius from that of said intermediate drum byan amount of 10 μm or more.
 4. The head drum device according to claim1, characterized in that the carbon content of said synthetic resin is10 percent or more by weight.
 5. In a magnetic recording/playbackapparatus for performing either or both recording and playback of asignal on a magnetic tape, said magnetic recording/playback apparatus ischaracterized by having a head drum device comprising: a fixed lowerdrum including a lead for helically guiding said magnetic tape; anintermediate drum including a magnetic head on the outer peripheralsurface thereof, which is rotated and supported coaxially with saidlower drum and is formed in such a manner that the axial length of saidouter peripheral surface is smaller than the width of said magnetictape; and an upper drum made of a synthetic resin containing carbon,which is fixed and supported coaxially with said intermediate drum.